Optical systems, such as telescopes, often require optical paths of specific lengths, such as focal lengths of optical elements. To reduce physical size of an optical system, an optical path may be folded one or more times by one or more reflecting elements, typically mirrors. Some folded optical systems, such as early Newtonian telescopes, dispose one or more of the reflecting elements within an optical path, thereby obstructing a portion of the optical path. Judicial placement of reflecting optical elements can, however, yield unobstructed folded optical systems.
Traditional unobstructed multi-reflection telescopes utilize three or more mirrors to correct and maneuver a ray bundle between an aperture and an image sensor, eyepiece or other output device. However, such telescopes are relatively physically large. More compact telescopes are desirable, such as when they are used on artificial satellites or other space vehicles.